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Item The effects of shading and defoliation on the nodulation and nitrogen fixation of white clover (Trifolium repens L.): a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science at Massey University(Massey University, 1971) Chu, Alexander Cheong PingThe ability of the legume-Rhizobium symbiosis to fix atmospheric nitrogen, hence contributing towards the maintenance of soil fertility is well recognised. Although increasing usage of mineral nitrogen is evident in agricultural practices overseas (Watkin, Williams 1970), in New Zealand legume nitrogen is still by far the most important source of nitrogen in grassland farming. Nitrogen fixation in a fertile ryegrass-white clover association has been estimated to yield as much as 550 1b N Per acre per annum (Sears 1953), and it has been emphasised that for maximum benefit to the grass component in a mixed sward the white clover should be periodically defoliated and have ample light for regrowth (Butler, Greenwood &Soper 1959). The present study examines the effects of defoliation and shading on nodulation and nitrogen fixation in white clover.Item The effects of nitrate nitrogen and phosphate on the nodulation and nitrogen fixation of white cliver (Trifolium repens L.): a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science at Massey University(Massey University, 1974) Fillery, Ian R. PIt is a well established fact that the presence of nitrate ions can depress nodule development on legume roots, but recent studies in Queensland (Gates, 1970) have shown that this sensitivity can be ameliorated if phosphate levels are maintained at a high rate. Gates studies involved tropical legumes and their appropriate rhizebial symbionts, and this study was conducted to ascertain whether a similar situation obtains with a temperate species like Trifolium repens (White Clover). Quantitiative information on the effect of nitrate nitrogen and phosphate on nitrogen fixing activity in white clover was also lacking, and an attempt was made to rectify this deficiency by examining the changes in rate of ethylene production per plant or mg nodule (dry weight) with the application of nitrate nitrogen and higher rates of phosphate.